1. Field of the Invention
The present invention relates to a constant speed cruising control apparatus for an automobile for keeping cruising speed for the automobile.
2. Discussion of Background
FIG. 6 is a diagram of a conventional constant speed cruising control apparatus for an automobile disclosed in, for instance, Japanese Unexamined Patent Publication 39311/1983.
In FIG. 6, a reference numeral 1 designates a set switch for instructing the start of constant speed cruising by a driver, a numeral 2 designates a cancel switch actuated by operating a braking device (not shown) to release the constant speed cruising, a numeral 3 designates a car speed sensor to detect the cruising speed of the automobile, which is constituted by a rotating body 3a having four magnetic poles rotated by a meter cable (not shown) for transmitting revolution of a transmission unit (not shown) and a read switch 3b and which is adapted to output pulse signals having a frequency in proportion to the cruising speed, a numeral 4 designates a battery for an automobile, a numeral 5 designates a main switch as a power source switch for supplying electric power in the battery 4, and a numeral 6 designates a control unit which includes a processing circuit 6a such as a microcomputer and which is operated by closing the main switch 5. The processing circuit 6a is adapted to receive signals from the set switch 1, the cancel switch 2 and the car speed sensor 3, and to perform processing operations for automatic control to coincide the actural cruising speed Vs with a target speed Vr to thereby output various control signals.
A motor-driven type throttle actuator 7 is provided in the intake air conduct 8 for the engine (not shown), which is adapted to receive the various control signals from the control unit 6 and to drive to open and close a throttle valve 9 in association with an accelerator pedal (not shown). The driving of the throttle valve 9 is performed through a wire 7b and a link 7a connected to a motor (not shown). An angle of rotation of the link 7a corresponding to the degree of opening of the throttle valve 9 is detected by a potentiometer (not shown) and the value of the angle is supplied to the control unit 6 as a signal indicative of the position of the throttle valve. The link 7a is connected to the motor through an electromagnetic clutch (not shown) and they are connected or disconnected by an electromagnetic crutch singal from the control unit 6.
The operation of the conventional constant speed cruising control apparatus having the above-mentioned construction will be described.
When a driver operates the main switch 5 to supply an electric power from the car battery 4 to the control unit 6, the control unit 6 is actuated to operate the output of the car sensor 3. The car sensor 3 outputs a train of pulse signals having a frequency in proportion to the actual car speed Vs during the cruising. The frequency of the pulses is measured by the control unit 6 to obtain the value of the cruising speed Vs. In the cruising, when the driver operates the set switch 1, a signal is supplied to the control unit 6, so that the cruising speed is stored as a target speed Vr in the control unit, and control of constant speed cruising or the car is initiated.
The actual cruising speed Vs of the automobile is measured periodically, and the signals indicative of the cruising speed Vs are compared with the target speed Vr in the control unit so that control signals are outputted to the throttle actuator 7 to adjust the degree of opening of the throttle valve 9, whereby the automobile runs at the target speed Vr. Namely, when the actual cruising speed Vs is lower than the target speed Vr, the throttle valve is opened by an amount to be required by a driving signal to open the throttle valve. Contrary, when the actual cruising speed Vs is higher than the target speed Vr, control of the throttle valve 9 is made to close it by an amount required. Thus, the automobile runs at a constant speed without operating the accelerator pedal by the driver.
When the driver operates a braking device while the control of the constant speed cruising is carried out, the cancel switch 2 is actuated, and a signal for releasing the constant speed cruising is supplied to the control unit 6. On receiving the signal, the control unit 6 immediately outputs a signal to disconnect the electromagnetic, clutch to the throttle actuator 7 to thereby release the electromagnetic clutch. After that, the driver adjusts the degree of opening of the throttle valve 9 by operating the accelerator pedal to control the cruising speed of the automobile.
On the other hand, when an automatic speed-changing device with an overdrive unit 12 is mounted on the automobile, and the automobile is on an uphill load under the constant speed cruising control, it is difficult to maintain the target speed Vr, and an overdrive cruising prohibiting signal 11 is outputted from the control unit 6 to the automatic speed-changing device 12.
Similarly, the overdrive cruising prohibiting signal 11 is outputted when an acceleration switch 10 is continuously operated beyond a predetermined time.
A numeral 13 designates a switch for changing an overdrive cruising prohibiting operation to a cruising operation and vice versa. The switch 13 allows the above-mentioned operation only when it permits the overdriving of the automobile.
In the conventional control apparatus, when the automobile was in such condition that it was on the uphill load under the constant speed cruising control, the throttle valve was opened to maintain the target speed and the overdrive cruising prohibiting signal was outputted. At the moment when the automatic speed-changing device 12 shifts the transmission system downwardly as soon as the overdrive cruising prohibiting signal is received, there takes place a shock in the automobile due to the speed changing. Also, the automobile undergoes a shock due to the speed changing in the case that the automobile is on a flat road just after finishing the uphill road cruising, at which time the overdrive cruising prohibiting signal is removed and the automatic speed-changing device 12 changes again to the overdrive operation.